Studies on the application of alteration in genome size to rice breeding

为了获得核DNA含量发生改变的二倍体水稻植株，利用人工同源四倍体水稻（Oryza sativa L.）CV. Nipponbare和Yunnishiki）在几代人中反复暴露于伽马射线。在种群中偶尔会出现与原始二倍体植株外观无差异的植株。到目前为止，获得了9个二倍体植株。结果表明，四倍体辐射诱变株系的核DNA含量的变异范围比二倍体（Norin 8）和日本栽培品种的核DNA含量变异范围大。此外，原始品种（Nipponbasare和Fukunioshiki）的DNA量变化方向是双向的，而许多突变株系的DNA量变化方向是双向的。 ...更多信息 在突变性状的研究中发现，四倍体辐射技术可在一株植物中同时诱发多个遗传性状的突变。我们研究了这些突变性状之间的相关性以及DNA含量与性状之间的相关性。众所周知，株高的变化与穗粒数、粒重等农艺性状的变化是同步的，这些变化被解释为突变基因的多效效应，而这些副作用通常是负的。本研究结果表明，四倍体辐射技术可以独立改变这些性状，突变性状与DNA含量无关。结果表明，基因突变对表型的影响比基因组大小的影响更为显著。我们认为，在DNA含量改变的过程中，染色体重排也会改变基因系统。进一步的研究将揭示所涉及的机制。少

In order to obtain the diploid rice plants with altered nuclear DNA content, populations of artificial autotetraploids of rice ( Oryza sativa L. cv. Nipponbare and Fukunishiki ) were repeatedly exposed to gamma-rays through several generations. Plants which did not differ in appearance from the original diploid plants occurred occasionally in the populations. So far, 9 diploid plants were obtained. These plants were advanced their generations without irradiation in order to examine the segregation of characteristics and the variation of nuclear DNA content.In the experiments, it was revealed that the mutant strains obtained through tetraploid-irradiation technique had wider range of variation in nuclear DNA content than the mutant strains obtained by irradiation of diploid plant (Norin 8) or Japanese cultivares had. In addition, the direction of changes in DNA amount from those of original cultivares (Nipponbasare and Fukunioshiki) was both directional, whereas many of the mutant strai … More ns obtained by irradiation of diploid plants (Norin 8) reduced their DNA amount.In the investigation of mutated characters, it was indicated that several mutations of qualitatively and quantitatively inherited characters were induced in a single plant simultaneously through the tetraploid-irradiation technique. We examined the correlations among those mutated characters and also between DNA amount and the characters. It is well known that the plant height changes simultaneously with several agronomic characters such as number of spikelet per panicle, grain weight and so on. It is reported that these findings were interpreted as pleiotropic effect of a mutant gene, and these side effects were usually negative. The present results, however, suggest that these characters can be altered independently by using tetraploid-irradiation technique.The mutated characters were not correlated with DNA amount. The findings suggest that the genic mutations have more marked effects on phenotype than the genome size have. We considered that the genic systems are also altered through chromosome rearengement in the process of changing DNA amount. Further investigations will reveal the mechanisms involved. Less